The need to store digital files, documents, pictures, images and other data continues to increase rapidly. As a result, the demand for data storage continues to increase. In addition, recent legislation, such as the Sarbanes-Oxley Act in the United States, affecting the management of electronic records, has increased the need for data storage. As the demand for data storage has increased, the space or volume occupied by storage systems has become an important issue. In particular, data storage having high capacity, high density, and space efficiency has become increasingly desirable.
In order to provide increased storage space, storage devices with ever greater storage capacities are being developed. However, the storage needs of even small enterprises can easily exceed the storage capacity of a single data storage device. In addition, in order to safeguard data, systems providing data redundancy that include multiple storage devices are necessary.
Systems that provide at least some integration of individual storage devices, such as JBOD (just a bunch of disks), SBOD (switched bunch of disks) or RAID (redundant array of independent (or inexpensive) disks) systems have been developed. Such systems are typically deployed within enclosures to present an integrated component to the user. The typical enclosure features very tight drive packaging, leaving little space for controllers if the system provides a RAID array, or an interface card if the system provides a JBOD or SBOD system. Furthermore, with the development of higher RPM (e.g., 10,000 RPM and 15,000 RPM) hard disk drives and reduced (e.g. 1 inch) drive packaging, the thermal densities of state of the art storage enclosures have increased. In addition, the dense packaging of multiple storage devices creates serviceability and/or cooling problems. For example, storage devices within an enclosure are commonly interconnected to trays or sleds that facilitate the insertion and removal of devices from the enclosure. For example, in connection with an enclosure adapted for use as part of a rack or stack of multiple enclosures or other devices, the sleds can be arranged so that they are removable through the front panel of the enclosure. Furthermore, the sled is typically implemented as a field replaceable unit (FRU) such that even relatively unsophisticated personnel can exchange failed components for replacements. That is, the sled and any attached disk drives are replaced as a unit, rather than removing a failed disk drive from the sled, and attaching a new disk drive to the sled. In order to maximize the storage density of a storage device enclosure, multiple disk drives would need to be interconnected to each sled. Accordingly, in connection with systems featuring more than one disk drive on a sled, the replacement of a failed disk drive typically results in the removal of a functional storage device. Furthermore, while most RAID arrays providing data redundancy can tolerate a single drive failure, data is lost or will be unavailable if more than a single data storage device is removed from a typical RAID array. Therefore, removing a sled to service one of a number of interconnected drives can result in the removal of data from the system. Accordingly, systems featuring multiple disk drives per sled present serviceability and maintenance problems.
The high packaging densities that can be achieved by interconnecting multiple disk drives to a sled, and by providing a number of such disk drives within an enclosure, also presents cooling problems. Although storage system enclosures typically include one or more cooling fans, maximum cooling capacity is eventually limited by the volume within the enclosure available for the passage of cooling air. This problem can be addressed by adopting more elaborate cooling techniques, such as liquid cooling. However, such alternatives to air cooling can dramatically increase the cost of the storage system.
In order to reduce the amount of power consumed by storage devices, systems that allow storage devices to be powered down have been developed. In a typical power saving system, a storage device is powered down if it has not been used to store or access data for a predetermined period of time. In general, such systems have been used in connection with battery powered computing devices in order to extend battery life. However, such techniques have generally not been adapted to data storage systems featuring a number of storage devices. In particular, such systems have typically used hard disk drive type storage devices in order to provide fast access to data. However, powering down a hard disk drive can dramatically increase access times, because a hard disk drive must be spun up before data can be accessed. In addition, such storage devices are typically line powered, and therefore power consumption is not a major concern. As a result, powering down disk drives has generally not been thought to be practical in connection with relatively high density storage systems.
In addition to storage systems that utilize a number of hard disk drive type storage devices, systems using other storage media have been developed. For example, systems using reels or cartridges of magnetic tape have long been used for storing large amounts of data. In addition to providing reels or cartridges that are always associated with a read/write head, tape libraries have been developed in which robotic actuators are used to retrieve tapes having desired information. Although tape based storage systems are generally characterized by much longer access times than disk type storage systems, the access times have been considered acceptable when tape based systems are used for “near line” applications, where near instantaneous access is not required. However, tape based storage systems have remained relatively expensive and can require a large amount of space. Accordingly, applications for tape based storage systems have generally been limited to large main frame computer systems. Furthermore, with the steady introduction of advances in the capacities of magnetic disk and optical disk type storage devices, and as the cost per megabyte of disk drives has gotten closer to that of tape based storage systems, tape based storage systems have become less desirable, particularly in view of the faster response times of disk based systems.